Conventional polarization beam splitters are used in a vast number of optics applications. These devices perform the function of separating s-polarized light and p-polarized light. Polarizing beam-splitters are essentially commonplace optical components and are currently widely used in optical instruments, lasers, electro-optic displays, optical recording and in the fabrication of other optical components. There are several parameters that can be used to describe the performance of a polarizing beam-splitter. These parameters are: the wavelength range over which the polarizing beam-splitter is effective, the angular field of the incident light in which the polarizer or polarizing beam-splitter is effective and the extinction ratio of the desired polarized light to the unwanted polarized light after the light passes through polarizing beam-splitter.
Commonly available polarizing beam-splitters can be divided into several types that depend upon different physical principles: pile-of-plates polarizers, reflection polarizers, Polaroid sheet polarizers, polarizers based on birefringent crystals, metallic grid polarizers, and thin film interference polarizers.
The instant invention is concerned with polarizing beam splitters (PBSs) based on birefringent crystals that perform well over a broad band of wavelengths and a wide range of angles. Normally these PBSs are comprised of a birefringent crystal prism. The optical axes of the prism are such that a lower refractive index exists along one axis for the ordinary light (polarized in one direction) and a higher refractive index exists along another axis for the extraordinary light (polarized in the other direction), or vice versa. Therefore, a very high extinction ratio is achieved. Many different arrangements for such PBSs exist. However this type of PBS is has generally been relatively costly; furthermore, they cannot be made in large sizes because of the limited availability of birefringent crystal materials.
Conventional PBSs using a single birefringent crystal have required provision of a collimated beam at the input end face of the crystal, therefore a lens has been provided before the crystal to provide the collimated beam. This design is seen to be a disadvantage.
It is therefore an object of this invention to overcome some of the disadvantages of conventional PBS designs, using a birefringent crystal.
It is a further object of this invention to provide a PBS that only requires a relatively small birefringent crystal.